1. Field of the Invention
The present invention relates to an ink tank that holds ink to be supplied to a recording head mounted on an ink-jet recording apparatus adapted to discharge the ink from the recording head to perform recording. The present invention further relates to an ink supplying apparatus for supplying ink to a recording head.
2. Description of the Related Art
An ink-jet recording apparatus has an ink-jet type liquid discharge head (hereinafter referred to as “the print head”) mounted on a carriage. When the carriage moves in a scanning manner from one end to the other end across a print medium, such as paper, film or fabric, a control system controls the print head to inject ink droplets onto the print medium so as to form a desired image and characters.
The ink is supplied to the print head from an ink supply source that moves together with the carriage or an ink supply source (liquid accommodating container, such as an ink tank) provided on a main body of a printing system that does not move together with the carriage.
If the ink supply source does not move together with the carriage, then the ink supply source connects an ink supply tube, which is used for continuously replenishing ink to the print head, to the print head thereby to replenish the ink.
The ink can be replenished also by positioning the print head at an ink replenishing station that permits easy connection between the print head and the ink supply source so as to intermittently connect the print head with the ink supply source, as necessary.
The ink supply source adapted to move together with the carriage is mounted on the carriage such that the ink supply source and the print head can be separated, and the ink supply source is replaced when it runs out of ink.
The print head is replaced when its service life expires. The ink supply source may be made integral with the print head. In this case, the whole assembly of the print head and the ink supply source is replaced when the ink runs out.
It is important for the ink supply source to reliably supply ink to the print head regardless of the position of the ink supply source in the printing system.
For the print head to properly function, it is essential to supply ink without interruption and to generate and maintain a negative pressure in the ink supply source and/or the print head.
The aforementioned negative pressure is a pressure in the print head that is negative relative to atmospheric pressure. If the negative pressure is excessively high, the concave surface of an ink meniscus in an orifice of a nozzle assembly through which ink is discharged becomes excessively large. This causes air bubbles to be easily captured after the ink is discharged, leading to discharge failure.
If the negative pressure is excessively low, the interfacial force by the surface tension of the ink at the orifice is exceeded, causing leakage of the ink. For this reason, the negative pressure is required to maintain the head pressure involved in the supply of the ink at a lower level than the atmospheric pressure so as to prevent the ink from leaking from the ink supply source or the print head.
It is required to apply a certain negative pressure to the ink supply source and/or the print head over a wide range of temperatures to which the printing system is subjected during its storage or operation and also over a wide range of atmospheric pressures. As an ink supply apparatus to meet the requirement, there is an ink-jet recording apparatus disclosed in Japanese Patent Laid-Open No. 2001-187459 (corresponding U.S. Pat. No. 6,520,630).
Similar configurations have been disclosed in Japanese Patent Laid-Open No. 2001-246761 and Japanese Patent Laid-Open No. 2001-130024 (corresponding U.S. Reference Nos. 6402306, 6460985, 6464346 and 2001009432) and their advantages have been described. Another conventional ink tank is shown in FIG. 6.
FIG. 6 is a sectional view showing a first conventional example of an ink supply apparatus.
The interior of an ink tank 12 is separated by a wall into an ink chamber 13 for holding an ink 14 in a free state and an ink absorber chamber 15 for accommodating an ink absorber 16 for absorbing the ink.
The ink tank bottom side of the wall is in communication with the ink chamber 13 and the ink absorber chamber 15 through the intermediary of a communicating portion. A plurality of grooves 24 extending to the communicating portion is formed in the wall in the vertical direction.
The ink absorber 16 is constructed of a member, such as a porous member or a fiber member, that generates a capillary force.
An optical reflective member 20 for detecting the residual quantity of the ink is disposed on the inner surface of the bottom portion of the ink chamber 13.
The ceiling portion of the ink chamber 13 has an ink inlet 17 through which the ink 14 is poured in. The ink inlet 17 is connected to an ink supply tube (not shown) and shut off from the atmosphere.
The ceiling portion of the ink absorber chamber 15 has an atmosphere communicating hole 18 for communication between the ink absorber chamber 15 and the atmosphere.
A print head 11 is provided on the bottom portion of the ink absorber chamber 15.
A filter 19 is provided in an ink passage 22 connecting the ink absorber chamber 15 and a head liquid chamber 21 of the print head 11.
The ink absorber 16 in the ink absorber chamber 15 functions as a buffering means against changes in ambient environments. For instance, if an ambient air pressure drops or an ambient temperature rises, the air in the ink chamber 13 expands. In this case, the ink in the ink chamber 13 equivalent to the air expansion moves through the intermediary of the communicating portion, and the ink absorber 16 in the ink absorber chamber 15 absorbs the ink, thus making it possible to apply a proper negative pressure to the print head even when environmental changes take place.
The grooves 24 provided in the partition between the ink chamber 13 and the ink absorber chamber 15 permit easy movement of the ink and the air between the ink chamber 13 and the ink absorber chamber 15 so as to allow stable ink supply to be accomplished and also allow air bubbles to be easily separated when the air bubbles move into the ink chamber 13 when supplying the ink.
FIG. 7 is a sectional view showing a second conventional example of the ink supply apparatus.
The description of the second conventional example will be mainly focused on aspects that are different from the first conventional example.
The ink supply apparatus shown in FIG. 7 is different from the apparatus shown in FIG. 6 in that an ink absorber in an ink absorber chamber 15 is composed of two ink absorbers 16b and 16c having different densities. The bottom of an ink tank 12 is provided with a joint 30 to be connected with a print head 11. The interior of the joint 30 provides an ink lead-out passage for leading out the ink from the ink absorber chamber 15, an ink absorber 16a being disposed in the ink lead-out passage.
The ink absorber 16a restrains ink leakage and makes the print head 11 and the ink tank 12 detachable. The print head 11 has an ink passage 22 to be connected to a head liquid chamber 21, the ink passage 22 being connected to an ink lead-out passage of the joint 30 through the intermediary of the filter 19. A gasket member 25 disposed between the joint 30 and the print head 11 prevents ink leakage from between the joint 30 and the print head 11.
The ink absorber 16c in the ink absorber chamber 15 functions as a negative pressure control means when ambient environments change. For example, if air pressure drops or the temperature in the ink tank 12 rises, the pressure of the air in an upper layer portion of the ink chamber 13 that stores ink in a free state becomes relatively higher. As a result, the amount of ink equivalent to the volume of the expanded air is pushed out of the ink chamber 13 into the ink absorber chamber 15 and absorbed by the ink absorber 16c through the intermediary of grooves 24. This makes it possible to maintain a negative pressure within a proper range without applying an excessive positive pressure to the print head 11 when an internal pressure changes.
The density of the ink absorber 16a is higher than that of the ink absorber 16b, and its strong capillary force draws the ink into the print head 11 and also restrains ink leakage. The capillary force of the ink absorber 16b is stronger than that of the ink absorber 16c to make it difficult for ink to remain in the ink absorber 16c toward the end of use of the ink tank 12. The ink tank 12 is led by a guide or the like (not shown) to the print head 11 and detachably and hermetically connected thereto by the gasket member 25.
FIG. 8 is a sectional view showing a third conventional example of the ink supply apparatus. The description of the third conventional example will be focused primarily on aspects different from that of the first conventional example.
The ink supply apparatus shown in FIG. 8 differs from the apparatus shown in FIG. 7 in that the wall constituting an ink chamber 13 is provided with an air suction port 27 and an ink inlet 26. The air suction port 27 that draws in air from the ink chamber 13 is maintained in a hermetically sealed state with a valve. Connected to the ink inlet 26 is a flexible ink supply tube (not shown) for supplying ink 14 from a main tank fixed in a recording apparatus main body.
Japanese Patent Laid-Open No. 8-112913 has disclosed an example configuration for replenishing ink from a main tank to a sub tank. In the example, a suction pump performs an operation for restoring an ink discharge function of a print head and the same suction pump replenishes ink.
In the conventional ink supply apparatuses described above, ink is held by the capillary forces of the ink absorbers, so that the ink can be held or discharged only within the range of about 20% to about 70% of the volume of the ink absorbers, posing a problem of poor efficiency of use of the ink tank. If the ink tank is made larger to increase the amount of ink to be held in the ink tank in order to prolong the service life of the ink tank, then the amount of air that increases as the ink is consumed will increase accordingly. This would require the volume of an ink absorber functioning as a buffer, inevitably leading to a larger size of the ink tank.
Furthermore, a larger-capacity ink absorber would be required, so that more wastes would result when the ink tank is disposed of, or a dye, which is a dissolved component in a liquid, may coagulate in an extended storage of the ink tank. Moreover, requiring an ink absorber having a larger capacity would lead to increased manufacturing cost of a replacement ink tank. In addition, to supply ink from a main tank into an ink chamber of an empty ink tank, a separate air suction means would be necessary to draw out the air in the ink chamber 13 through the air suction port 27, as illustrated in FIG. 8.
If the ink is drawn in from a nozzle assembly to replenish ink into the ink chamber, as another means, then a large amount of redundant ink would be drawn in and consumed. Even if the excess ink that has been drawn in is recycled, measures against dust and an additional ink passage would be required. Hence, this means is not a good solution.